A serious problem which is encountered with seat belt assemblies and which has been well recognised but not yet solved is that a seat belt assembly can be loaded with what is herein termed the "first stage of overload", and which can for example be nine kilonewtons although at this time no numerical load has been identified by authorities. When so loaded, it is possible for the webbing to become strained or the latching mechanism to be damaged to a point where absolute security is uncertain and the seat belt should be replaced. Such a situation can occur for example if a vehicle is involved in a minor accident and the seat belt assembly has "held", protecting a wearer against displacement, and it is important that the wearer should be able to subsequently release that belt. There is of course a second stage of overload which occurs beyond the first stage of overload wherein the belt will become obviously damaged and unworkable.
The main object of this invention is to provide means whereby the seat belt assembly can be readily identified as having been subjected to the first stage of overload even though it is still operable.